| The accelerator driven sub-critical system(ADS)has been universally regarded as the the most promising approach to dispose the nuclear wastes.It has the performance of large neutron flux and powerful transmutation ability.It also has the inherent safety and can output extra energy so as to improve the utilization of fuel.The Institute of Modern Physics,Chinese Academy of Sciences(IMP,CAS)has proposed a new concept of ADS with the gravity-driven dense granular target,where the study of the neutronics is very important.For lack of accurate and reliable neutron nuclear data,the neutronics study plays an important role in the design of the new concept of ADS.The integral neutronics experiments of silicon carbide,graphite,uranium and polyethylene,used in the ADS,were conducted at the Key Laboratory of Nuclear Data,China Institute of Atomic Energy.In order to study the neutron transportation performance in the target coupled with the ADS core,a simplified multiple-slab sample assembly was built.The leakage neutron spectra from multiple-slab sample assemblies comprising W,U,C,and CH2 were also measured.The results obtained were compared with calculation performed employing the Monte Carlo neutron transport code MCNP with the CENDL-3.1,ENDF/B-VII.1,JENDL-4.0,JEFF-3.2,FENDL-3.0 and TENDL-2015 libraries.The CENDL-3.1 library was benchmarked for the first time.The leakage neutron spectra from SiC samples at 60° and 120° has been experimentally measured by using TOF method.For the leakage neutron spectra of 20 cm SiC at 60°,the calculated results with CENDL-3.1,JENDL-4.0,FENDL-3.0 and TENDL-2015 libraries show better agreements above 8 MeV,while the JEFF-3.2 calculations reproduce the measured results well below 8 MeV.For 20 cm SiC at 120°,the calculations based on FENDL-3.0 library agree well with the measured results in 1-15 MeV.For 2cm SiC at 60°,the calculations based on CENDL-3.1,JENDL-4.0 and FENDL-3.0 libraries reproduce the measured results well in 1-16 MeV.The dimentions and measured angles of graphite were the same as silicon carbide.The calculations based on CENDL-3.1,JENDL-4.0,FENDL-3.0 and TENDL-2015 libraries reproduce the measured results well in 1-15 MeV.However,all of the calculations are greatly overestimated in the energy range of 5-7 MeV.Besides,the neutron nuclear data of graphite from FENDL-3.0 are the same as from TEND1-2015.The leakage neutron spectra of 2 cm and 5 cm uranium was measured at 60°.For 2 cm U,the calculations based on ENDF/B-Ⅶ.1,JENDL-4.0 and FENDL-3.0 libraries reproduce the measured results well below 10 MeV,while the TNEDL-2015 calculations show better agreements above 10 MeV.For 5 cm U,the calculations based on JENDL-4.0 library agree well with the measured results in 1-16 MeV.Besides,the neutron nuclear data of uraniun from FENDL-3.0 are the same as from ENDF/B-Ⅶ.1.The multiple-slab sample assemblies of "W-U-C-CH2" and "U-C-CH2" were built up gradually as "U,W+U,W+U+C,W+U+C+CH2" and "U,U+C,U+C+CH2".The leakage neutron spectra were measured at 60° for the first time.With the multiple-slab samples added,the discrepancies between the calculated and the measured results were decreasing.From the comparison between the results of"W+U+C”and "W+U+C+CH2",the C/E ratios became consistent with 1.0 when CH2 was added to the target.A significant phenomenon was observed that the secondary neutrons,which were generated by D-T neutrons bombarding on multiple-slab samples,were moderated and reflected to low energy region.This work achieves the benchmark test of the evaluated nuclear data libraries and provides the most suitable library for the calculation.It also provides valuable data to facilitate future studies of neutron transportation in the target coupled with the ADS core as well as the design of the ADS. |
